1. Technical Field
The present invention relates to a switch circuit and a single pole double throw (SPDT) circuit, and more particularly, to a switch circuit and an SPDT circuit capable of improving insertion loss characteristics by varying a resistance value of a gate resistor of a metal oxide semiconductor (MOS) transistor.
2. Description of the Related Art
In accordance with the development of a wireless communication technology, 4G mobile communication such as long term evolution (LTE) in addition to the 3G mobile communication has emerged. As a function of the 4G mobile communication network has been added to existing 2G and 3G mobile communication networks, a frequency band that should be supported by one cellular phone has gradually increased.
In order for one cellular phone to cover a wide frequency band, a single pole multi throw (SPMT) switch using a metal oxide semiconductor field effect transistor (MOSFET) has been used.
In this case, insertion loss characteristics of the switch should be excellent in order to decrease loss of a system, and isolation characteristics of the switch should be excellent for stability of the system.
A general flow of a signal passing through a switch using the MOSFET will be described below. A gate resistor Rg of the MOSFET serves to suppress signals leaked through a gate. Therefore, as a resistance value of the gate resistor becomes large, the leakage of the signals is decreased, such that many signals are transferred to an output. As a result, insertion loss is decreased.
However, when the resistance value of the gate resistor is large, a switching time is increased to cause a problem in a system operation. Therefore, as the gate resistor, a resistor having a large value may not be unconditionally used. Here, the switching time may be represented by the product of gate resistance and gate capacitance. Therefore, a magnitude of the resistance value of the gate resistor is limited by the switching time. In this case, generally, a fixed gate resistor is used, and a magnitude of a resistance value is determined to satisfy the switching time of the MOSFET.